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Abstract
Rifting in the Gunsan Basin between China and Korea started in late Mesozoic times, due to large-scale interaction between the
Pacific, Eurasian and Indian plates. To analyze the detailed tectonic evolution of this basin, backstripping the subsidence history of
four representative units in the basin has been undertaken including sag and half-graben structures in the Central sub-basin as well
as half-graben and graben structures in the SW sub-basin. Backstripping indicates that the subsidence history of the Gunsan Basin
can be grouped into a Late Cretaceous-Oligocene a main subsidence phase and a Middle Miocene-present secondary subsidence
phase. These phases were separated by an uplift and erosion phase during early Miocene times. The main subsidence phase com-
prised a rapid Late Cretaceous-Paleocene subsidence event and a slower Eocene-Oligocene subsidence event. These phases can
be correlated to seismic sequence MSQ I, II and III, identified in the SW sub-basin from seismic stratigraphy, and can further be
related to the convergence of the Pacific, Eurasian and Indian plates. Compared with the McKenzie (1978) lithospheric stretching
model, this basin is relatively similar to the typical tectonic subsidence characteristics of intracontinental basins.
Die Riftingphase im Gunsan Becken zwischen China und Korea begann im späten Mesozoikum als Produkt der Wechselwirkung
zwischen Pazifischer, Eurasischer und Indischer Platte. Um die detaillierte tektonische Geschichte des Beckens zu analysieren wurde
eine Backstripping-Subsidenzanalyse an vier repräsentativen Einheiten des Beckens unternommen welche, etwa. Mulden- und Halb-
grabenstrukturen im zentralen Teilbecken und Halbgräben und Gräben im südwestlichen Teilbecken beinhalten. Die Backstripping-
Methode zeigt, dass die Subsidenzgeschichte des Gunsan Beckens in eine Oberkreide-Oligozäne Hauptabsenkungsphase und eine
Mittelmiozäne-rezente sekundäre Absenkungsphase geteilt werden kann. Diese Phasen sind durch eine frühmiozäne Phase von Up-
lift und Erosion getrennt. Die Hauptabsenkungsphase teilt sich in eine Oberkreide-Paleozäne Phase rascher Subsidenz und einen
langsameren, Eozän-Oligozänen Abschnitt. Die unterschiedlichen Phasen können mit den seismischen Sequenzen MSQ I, II und III
korreliert werden, die im südwestlichen Teilbecken mit Hilfe von seismischer Stratigraphie identifiziert wurden, und können mit der
Konvergenz der Pazifischen, Eurasischen und Indischen Platte in Zusammenhang gebracht werden. Im Vergleich mit dem McKenzie
(1978) Modell lithosphärischer Dehnung kann das Becken mit der tektonischen Subsidenz intrakontinentaler Becken verglichen werden.
________________
KEYWORDS
Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea___________
Eun Young LEE
Department Petroleum Resources Technology, University of Science & Technology, Gwahangno 113,
Yuseong-gu, Daejeon, South Korea;
Current address: Department of Geodynamics & Sedimentology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria;
1. Introduction
The Yellow Sea, a semi-enclosed continental shelf basin si-
tuated between China and Korea (Fig. 1) consists of several
basins, including the Bohai, the North Yellow Sea, the South
Yellow Sea and the Subei basins. The South Yellow Sea Basin
is further subdivided into the Northern and Southern South Yel-
low Sea basins by a central uplifted area (Zhang et al., 1989).
The Gunsan Basin is the Korean portion of the Northern South
Yellow Sea Basin (Park et al., 1997) (Fig. 1 and 2).
During the last few decades, comprehensive research pro-
grams on the Gunsan Basin have focused primarily on oil ex-
ploration. However, the kinematic processes and geodynamic
evolution of this basin are far from being understood, although
the basin type and rifting processes have been discussed. Ma-
rathon (1987) developed a transtensional model for the rifting
mechanism. In contrast, Baag and Baag (1994) suggested a
suite of pull-apart basins associated with double-overstepped
left-lateral wrenches, although up to now, no major strike-slip
fault which might have caused rifting in the Gunsan Basin has
been found. More recently, Ren et al. (2002) suggested simi-
________
larities between intracontinental rift basins and the South Yel-
low Sea Basin.
The purpose of this paper is to establish some details of the
tectonic evolution of the Gunsan Basin. For the analysis, this
study focuses on backstripping the subsidence history of the
basin, which is useful for investigating the basin-forming me-
chanisms. One of the benefits of a complete decompaction
and backstripping procedure is that the subsidence history of
basins can be compared without the complications of different
paleobathymetric, eustatic, compactional and isostatic effects
(Allen and Allen, 2002).
East Asia comprises a mosaic of distinct continental frag-
ments separated by fold belts resulting from the accretion of
various fragments formerly separated by intervening areas of
oceanic crust (Watson et al., 1987). The Yellow Sea lies on the
Yangtze (South China) Platform and the Sino-Korean (North
China) Platform, sutured by the Qinling-Dabie-Sulu collisional
_____________________________________
_______________________________
2. Geologic Setting
Austrian Journal of Earth Sciences Vienna 2010Volume 103/1
Northern South Yellow Sea BasinSubsidence history
Gunsan BasinBackstripping
Yellow SeaKorea
belt during the early Mesozoic (Hsu,
1989; Gilder and Courtillot, 1997;
Kim et al., 2000; Wu, 2002).
Since late Mesozoic times, a large
number extensional or transtensio-
nal basins have developed in East
China, caused by large-scale inter-
actions between the Pacific, Eura-
sian and Indian plates (Ren et al.,
2002). In the Gunsan Basin, which
formed on the Yangtze Platform (Fig.
1), rifting started in the late Mesozo-
ic times. At 65 Ma, during the early
Late Cretaceous, the Pacific Plate
moved to the edge of eastern China
and changed its subduction velocity
and direction from NNW to WNW,
at a steep angle (Uyeda and Kana-
mori, 1979; Engebretson et al., 1985;
Maruyama et al., 1997). These chan-
ges led to an upwelling of the asthe-
nosphere and consequent thinning
of the lithosphere in eastern China
(Yu et al., 2008, Zhou and Li, 2000),
assisting the rifting process in eas-
tern Eurasia and resulted in Late
Cretaceous extensional tectonics.
The Gunsan Basin is divided into
three sub-basins by basement highs
and faults; the North-East (NE), Cen-
tral and South-West (SW) sub-basins
(Yi et al., 2003; KIGAM, 2006) (Fig.
2). The structure of the North-East
sub-basin is difficult to characterize
its structure due to problems with
defining its exact northeastern bor-
der: here, a few NW-SE trending
normal faults have been recognized
on seismic profiles close to the pre-
sumed basin margin. The NW-SE
trending Central sub-basin, which
lies between basement highs sepa-
rating it from the NE and SW sub-
basins, is further characterized by a
different structural style than in the
regions to the north and south. In
the south, it is a sag type basin with
gently sloping boundaries, whereas
in the north it is defined as a half-
graben structure with a rotated hang-
ing wall relatively down-thrown at the
bounding normal faults. The South-
West sub-basin includes both gra-
ben and half-graben structures that
developed along the E-W trending
______
_
Figure 2: . Geological setting of the South Yellow Sea Basin, separated into Northern and Sou-
thern South Yellow Sea Basins by the Central High. The Gunsan Basin is the Korean portion of the
Northern South Yellow Sea Basin in Korean shelf block 1 and 2. Locations of 5 exploratory wells ( )
and 4 artificial well sites ( ) for subsidence analysis (modified from PEDECO, 1997).
■
● _____________
Figure 1: Bathymetry of the Yellow Sea, and major Cenozoic basins (modified from Lee et al.,
2006). The Gunsan Basin is the Korean portion of the Northern South Yellow Sea Basin._________
Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea
southern bounding faults (Shin et al., 2005).
The sediment fill of the Gunsan Basin mainly consists of
Upper Cretaceous and Cenozoic non-marine (fluvial-alluvial
and lacustrine) clastic sediments with a thickness of several
kilometers. Erosion of the sediments deposited within the ba-
sin occurred during the Oligocene to Early Miocene, when the
basin was subjected to compression and inversion. Since the
middle Miocene, deposition has been dominated by mainly
unconsolidated sands (KIGAM, 2006, Yi et al., 2003).
Backstripping is a technique for progressively removing the
sedimentary load from a basin, correcting for compaction, pa-
leobathymetry and changes in sea level, in order to reveal the
tectonic driving mechanisms of basin subsidence. The proce-
dure for backstripping a sedimentary basin starts with the di-
vision of the stratigraphic column into increments for which
the thickness and age range can be accurately determined
(Miall, 2000).
This technique requires an inference on the variation of po-
______________
_______
_______________________________________
3. Data and Methods
rosity with depth, to enable the decompaction of stratigraphic
units to be calculated. This is taken to be a simple exponential
decrease with increasing depth, z, Ø= Ø exp(-cz) (Ø : the ini-o
tial porosity, c: the porosity-depth coefficient) (Sclater & Chris-
tie, 1980). Further, following Steckler & Watts (1978), water-
loaded basement subsidence, Y, is given by Y = S[(ρ -ρ )/(ρ -m s m
ρ )] + W - Δ [ρ /(ρ -ρ )] (S: sediment layer thickness correc-w d SL m m w
ted for compaction, Δ : sea-level change, Wd: water depth, at SL
burial time. ρ , ρ , and ρ : the mantle, mean sediment, and m s w
water densities).
The data for this work were collected by the Korea National
Oil Company (KNOC) and Korea Institute of Geoscience and
Mineral (KIGAM). The geological ages of the key unconformity
surfaces (acoustic basement, top of the Upper Cretaceous
(Maastrichtian), top of the Paleocene, top of the Eocene, bot-
tom of the Middle Miocene) recognized on seismic data were
taken directly from KIGAM (2006) and Park et al. (2005), which
are based on data from exploration wells (IIC-1X, IIH-1Xa,
Haema, Inga, and Kachi) in the Gunsan Basin.
In this area, porosity values calculated from the available
o
____________________________________
____________
Figure 3: Subsidence history and rates of sag and half-graben structures in the Central sub-basin.
Eun Young LEE
well data are not applicable because the results are unrealis-
tically high. Thus typical values for the subsurface porosity
and the porosity-depth coefficient were taken from published
general exponent data (Tab. 1). In this study, Δ and W pa-SL d
rameters used for water-loaded basement subsidence, were
not considered, because the Gunsan Basin sediments are
nonmarine with shallow paleobathymetries and negligible in-
fluences from sea-level changes. For this backstripping, the
above processes were calculated on a spreadsheets using of
Microsoft Excel.
To reconstruct the thickness of sediment eroded during the
_____________________________________
Early Miocene, the stratum thickness trend on eroded tilted
fault blocks on the seismic section of the Central sub-basin
were analyzed, based on the typical tectonic and stratigraphic
evolution. From this, the eroded thickness was estimated at
about 500 m.
To analyze the subsidence history, four “artificial wells” were
selected from typical seismic profiles of representative units
in the Gunsan Basin: these are the southern sag and northern
half-graben structures in the Central sub-basin, and half-gra-
ben and graben structures in the SW sub-basin (Fig. 2).
In the Central sub-basin, the southern sag and northern half-
graben structures are selected for reconstruction of the sub-
sidence history. The subsidence curves of the southern sag
structure can be divided into 6 segments (Fig.3): 1) Late Cre-
_______________________________________
____
____________________________________
4. Subsidence analysis of the Gunsan Ba-
sin
4.1 Subsidence analysis in the Central
sub-basin
Figure 4: Subsidence history and rates of half-graben and graben structures in the SW sub-basin.
Table 1: Exponents of Surface porosity (Ø ), Porosity-depth co-O
efficient (c), Sediment grain density (ρ ) for different lithologies (modi-sg
fied from Sclater & Christie, 1980).____________________________
Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea
taceous (Maastrichtian) (70.6-65.5 Ma), 2) Paleocene (65.5-
55.8 Ma), 3) Eocene (55.8-33.9 Ma), 4) Oligocene (33.9-23.03
Ma), 5) Early Miocene (23.03-15.97 Ma), 6) Middle Miocene-
Present (15.97-0 Ma). During the Late Cretaceous, the sub-
sidence curves are very steep, with subsidence rates of ca.
558 m/Ma for total subsidence and ca. 187 m/Ma for tectonic
subsidence. Paleocene subsidence curves are also steep, with
subsidence rates of ca. 182 m/Ma for total subsidence and ca.
45 m/Ma for tectonic subsidence. On the whole, sub-sidence
rates decrease gradually to ca. 45 m/Ma for total sub-sidence
and ca. 9 m/Ma for tectonic subsidence from the Late Creta-
ceous to Oligocene. In the Early Miocene, the curves rise and
show uplift and erosion. Again, from the Middle Miocene on-
wards, this structure subsides at a rate of ca. 30 m/Ma for to-
tal subsidence and ca. 7 m/Ma for tectonic subsidence.
The subsidence curves of the northern half-graben structure
can be divided into 5 segments (Fig. 3). Compared with the
subsidence curves in the southern structure of this sub-basin,
the subsidence curves in the north have no Late Cretaceous
segment. Subsidence started in the Paleocene with steep su-
bsidence curves indicating a subsidence rate of ca. 169 m/Ma
for total subsidence and ca. 67 m/Ma for tectonic subsidence.
Similar to the southern part, in the Oligocene, the subsidence
rate decreased steadily to ca. 41 m/Ma for total subsidence
and ca. 8 m/Ma for tectonic subsidence. In the Early Miocene,
uplift and erosion occurred, but from the Middle Miocene on-
wards, subsidence started again.
In the SW sub-basin, half-graben and graben structures are
_____
_______________________
4.2 Subsidence analysis in the SW sub-
basin
selected for calculation of the subsidence history. The subsi-
dence curves of these two structures can be divided into 6
segments (Fig. 4): 1) Late Cretaceous (Maastrichtian) (70.6-
65.5 Ma), 2) Paleocene (65.5-55.8 Ma), 3) Eocene (55.8-33.9
Ma), 4) Oligocene (33.9-23.03 Ma), 5) Early Miocene (23.03-
15.97 Ma), 6) Middle Miocene-Present (15.97-0 Ma).
In both the graben and half-graben structures, the subsidence
history shows a similar pattern. During the Late Cretaceous,
the subsidence curves are very steep, but become successi-
vely gentler towards the Oligocene. This indicates gradually
decreasing subsidence rates from Late Cretaceous to Oligo-
cene times. During the Late Cretaceous, subsidence rates in
the half-graben structure are ca. 341 m/Ma for total subsidence
and ca. 132 m/Ma for tectonic subsidence. This decreased to
ca. 27 m/Ma and ca. 8 m/Ma, respectively, in the Oligocene.
From the Late Cretaceous to the Oligocene, subsidence rates
in the graben structure of ca. 357 m/Ma for total subsidence
and ca. 136 m/Ma for tectonic subsidence decreased to ca.
30 m/Ma and ca. 10 m/Ma, respectively. During the Early Mio-
cene, a rise in the curves indicates uplift and erosion, but
from the Middle Miocene onwards, these structures started to
subside again.
The subsidence history of the Gunsan Basin is separated in-
to a main subsidence phase during the Late Cretaceous-Oli-
gocene and a secondary subsidence phase during the Middle
Miocene-Present, by the uplift and erosional phase of the Ear-
ly Miocene. The main subsidence phase consists of a rapid
subsidence and a slow subsidence event (Fig. 7).
_______
______________________________________
__________
5. The subsidence history of the Gunsan
Basin
Figure 5: S-N direction seismic profile showing MSQ I (Acoutstic basement-Paleocene), II (Eocene), III (Middle Miocene-Present) in SW sub-basin
(modified from Park et al., 2005).
Eun Young LEE
From the Late Cretaceous to the
Oligocene, the subsidence curves
of the basin become less steep do-
cumenting a steady decrease in the
subsidence rates. The subsidence
up to Oligocene times includes > 90
% of the total and tectonic subsiden-
ce that occurred in the Gunsan Ba-
sin. Hence this period is defined as
the main subsidence phase. Within
this, a rapid subsidence event (Late
Cretaceous-Paleocene) and a slow
subsidence event (Eocene-Oligoce-
ne) occurred. Tectonic subsidence
rates between 132-187 m/Ma occur-
red during the Late Cretaceous, and
between 17-67 m/Ma during the Pa-
leocene. Subsidence rates between
ca. 8-18 m/Ma occurred in the Eo-
cene-Oligocene.
The basin was inverted after the
Oligocene, with erosion during the
Early Miocene. This event defined
as the uplift and erosion phase, ter-
minated the main subsidence phase.
Since the Middle Miocene, the basin
has subsided again, at between ca.
5-12 m/Ma, defined as the secon-
dary subsidence phase.
Park et al., (2005) and Shin et al.,
(2005) delineated the geologic struc-
ture and seismic stratigraphy in the
SW sub-basin of the Gunsan Basin
through an interpretation of 2D seis-
mic data. These studies identified
12 unconformities in the SW subba-
sin and combined the formations in-
to 3 mega-sequences; MSQ I (Late
Cretaceous-Paleocene), MSQ II (Eo-
cene) and MSQ III (Middle Miocene-
Present) (Fig. 5). This classification
corresponds to the subsidence pha-
ses identified in this study.
The Late Cretaceous-Paleocene
rapid subsidence event is correlated
with MSQ I which was interpreted
as being formed from syn-rift sedi-
ments related to the development
of faults during a N-S trending ex-
tensional stress regime (Shin et al.,
2005). Most faults cut the Paleoce-
ne, but not the unconformably over-
lying Eocene (Fig. 6). This indicates
________________
__________
_______
6. Discussion
Figure 6: Time horizons structure maps of (a) top of basement, (b) late Paleocene unconformity,
(c) late Eocene unconformity (base middle Miocene unconformity) (modified from Park et al., 2005)._
Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea
that the tectonic driving force of basin rifting was very strong
in this period, and led to the high tectonic subsidence rates of
the rapid subsidence event.
The Eocene-Oligocene slow subsidence event correlates
with MSQ II (Eocene), which was characterized by post-rift
sedimentation. In this event, most faults cut the basement
and Paleocene, but are covered by the unconformably over-
lying Eocene (Park et al., 2005, Shin et al., 2005) (Fig. 6).
This indicates an abrupt decrease of tectonic driving force at
the end of the Eocene, and is related to the low tectonic sub-
sidence rates during the slow subsidence event.
Middle Miocene sediments unconformably overlie Eocene
sediments in the SW sub-basin and Oligocene sediments in
the Central sub-basin. Therefore, MSQ II does not include the
Oligocene period. In this study, it was assumed that the Oli-
gocene sediments originally deposited in the SW sub-basin
were entirely eroded during the early Miocene. Therefore, in
the subsidence analysis of the SW sub-basin, only Eocene
and Miocene sediments were included. Another explanation
for the lack of Oligocene sediments could be an earlier defor-
___________________________
___________
mation and uplift followed by erosion.
The secondary subsidence phase is equivalent to MSQ III
(Middle Miocene-Present). After the middle Miocene, regional
subsidence again led to widespread sedimentation. However,
few faults developed and the seismic reflections within strata
are consistent, parallel and continuous. This indicates that
this period was marked by tectonic quiescence and uniform
sedimentation.
Extension began in the latest Cretaceous along the east Eu-
rasian plate boundary (Northrup et al. 1995). This correlates
well with periods of reduced convergence rates between the
Pacific plate and Eurasia. This suggests a slowing of the con-
vergence rate between the Pacific and Eurasia plates during
early and middle Cenozoic times, which may have been rela-
ted to a decrease in the horizontal compressive stress trans-
mitted between the Pacific and Eurasian plates, as reflected
by widespread extension adjacent to the Eurasian margin at
this time. Ren et al., (2002) state that the Late Mesozoic and
Cenozoic rift systems in eastern Asia lie between two of the
most dynamic tectonic domains of the Earth’s lithosphere: the
___________________
______________________________________
subduction zones of the western Pa-
cific and the Tethys-Himalayan oro-
gen. The direction and rate of sub-
duction from the Pacific side and
subduction/collision along the Tethys
domain have changed several times
since the Mesozoic, which caused
the variation of stress fields in eas-
tern Eurasia in space and time. Rif-
ting in eastern Eurasia was caused
by changes of convergence rate and
direction in Pacific-Eurasia and India-
Eurasia movements.
Fig. 7 compares the subsidence
history of the Gunsan Basin with the
convergence rates of the major tec-
tonic plate boundaries. The Late Cre-
taceous convergence rate of the Pa-
cific-Eurasia plates was 120-140 mm/
year (Engebretson et al., 1985; North-
rup et al., 1995), when the stress field
of eastern Asia was characterized by
sinistral transpression (Tian and Du,
1987). The convergence rate decli-
ned substantially during the early
Cenozoic and reached a minimum
of 30-40 mm/year in the Eocene. In
contrast, the Late Cretaceous con-
vergence rate of the India-Eurasia
plates was about 100-110 mm/year
and increased during the early Ce-
nozoic and reached a maximum in
the Paleocene of 170-180 mm/year
at 65 Ma (Lee and Lawver, 1995).
This period corresponds to the ear-
____________
Figure 7: Subsidence phases of the Gunsan Basin
and convergence rate of plates. a) Subsidence phases
of the Gunsan Basin analyzed in this study, b) Conver-
gence rate of the Pacific-Eurasia plates (modified from
Engebretson et al., 1985; Northrup et al., 1995), c) Con-
vergence rate of the India-Eurasia plates (modified from
Lee et al., 1995)._______________________________
Eun Young LEE
ly Cenozoic rapid syn-rifting period of Eastern China (Ren et
al., 2002). In the Gunsan Basin, it corresponds to the rapid
subsidence and slow subsidence events, the former event, in
particular, is equivalent to an abrupt decrease of convergence
rate between the Pacific and Eurasia plates during the Late
Cretaceous and increase of convergence rate between the
India and Eurasia plates during the Paleocene (Fig. 7).
From Late Oligocene to Neogene times, the Pacific–Eurasia
convergence rate increased to an average of 100-110 mm/year
(Northrup et al., 1995), and the India-Eurasia convergence rate
decreased to 50 mm/year (Lee and Lawver, 1995). In this pe-
riod, extension stopped in eastern Asia, and many rift systems
in East China gradually evolved into a thermal subsidence
stage (Ren et al., 2002). And here, starting in the Late Eoce-
ne time, NNW movement of the Pacific plate changed to WNW
movement, due to the termination of oceanic subduction be-
neath the India-Eurasia collision zone (Ren et al., 2002, Pa-
triat and Archache, 1984). This corresponds to the uplift and
erosion phase and the secondary subsidence phase of the
Gunsan Basin (Fig. 7).
The tectonic subsidence curves of the Gunsan Basin (Fig. 3
and 4) are compared with the McKenzie (1978) lithospheric
stretching model in Fig. 8. The modeled curves were calcula-
ted for post-rift thermal subsidence resulting from lithospheric
re-equilibration after stretching and thinning. Tectonic subsi-
dence in the Gunsan Basin was less than 2 km, with subsiden-
ce curves approximately exponential in shape, and progressing
to simple thermal subsidence models of stretching factors ran-
ging from 1.1 to 1.3. Following Xie and Heller (2009), strike-
slip basins are characterized by rapid and short-lived (typi-
cally <10 m.y.) subsidence, but intracontinental basins have
relatively slow and long-lived (typically >200 m.y.) subsidence
histories. Further, most tectonic subsidence curves compiled
from intracontinental basins show < 2 km subsidence, appro-
ximately exponential in shape and broadly consistent with
simple thermal subsidence models of stretching factors (β)
_____
_______________________________
ranging from 1.1 to 1.5 (Xie and Heller, 2009).
1)
2)
3)
4)
5)
This research was supported by the Korea Institute of Geo-
science and Mineral Resources (KIGAM) funded by the Mi-
nistry of Knowledge and Economy. I would like to thank Prof.
Dr. Ko, Dr. Decker, two good reviewers and my colleagues in
University of Science & Technology and University of Vienna
for useful advices, comments, discussions and reviews.
____________
____
7. Conclusions
Acknowledgements
The Gunsan Basin, located between East China and West
Korea, is filled with mainly Upper Cretaceous and Ceno-
zoic non-marine clastic sediments. To analyze the subsi-
dence history, four sites were selected from representative
tectonic units, which comprise sag and half-graben struc-
tures in the Central sub-basin and half-graben and graben
structures in the SW sub-basin.
The subsidence history of the Gunsan Basin is grouped
into 3 phases; a main subsidence phase (Late Cretaceous-
Oligocene), an uplift and erosion phase (Early Miocene),
and a secondary subsidence phase (Middle Miocene-Pre-
sent). Further, the main subsidence phase consists of a
rapid subsidence (Late Cretaceous-Paleocene) and a slow
subsidence event (Eocene-Oligocene).
Compared with seismic stratigraphy studies of the SW sub-
basin, the rapid subsidence phase is equivalent to seismic
sequence MSQ I (Late Cretaceous-Paleocene) and is in-
terpreted as a period of syn-rift sedimentation. The slow
subsidence phase corresponds to MSQ II (Eocene) which
was characterized by post-rift sedimentation. The secon-
dary subsidence phase is equivalent to MSQ III (Middle
Miocene-Present).
The evolution of the Late Mesozoic and Cenozoic rift sys-
tems in eastern Asia may be linked to the convergence ra-
tes of the Pacific-Eurasia and also the India-Eurasia plates.
The subsidence history of the Gunsan Basin shows that
the main subsidence phase occurred during a decreasing
convergence rate of the Pacific-Eurasia plates and an in-
creasing convergence rate of the India-Eurasia plates. The
uplift and erosion phase and the secondary subsidence
phase are related to increasing convergence rate of the
Pacific-Eurasia plates and a decreasing convergence rate
of the India-Eurasia plates.
Tectonic subsidence curves of the Gunsan Basin show less
than 2 km subsidence, approximately exponential in shape
and progressing to simple thermal subsidence models of
stretching factors ranging from 1.1 to 1.3. This is relatively
similar to the typical tectonic subsidence characteristics of
intracontinental basins, rather than strike-slip basins.
_____________________
________________
________________________________
_________________________
_____
Figure 8: Comparison of tectonic subsidence curves of the Gunsan
Basin (from Fig. 3 and 4) with post-rift thermal subsidence curves cal-
culated from McKenzie (1978). Black lines are the tectonic subsidence
curves of the Gunsan Basin and gray lines are for thermal subsidence
curves calculated for differing β values._________________________
Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea
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Received: 22. December 2009
Accepted: 25. March 2010
Eun Young LEE
Department Petroleum Resources Technology, University of Science &
Technology, Gwahangno 113, Yuseong-gu, Daejeon, South Korea;
Current address: Department of Geodynamics & Sedimentology, Univer-
sity of Vienna, Althanstrasse 14, 1090 Vienna, Austria;
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Subsidence history of the Gunsan Basin (Cretaceous-Cenozoic) in the Yellow Sea, offshore Korea
